1. Technical Field
The invention relates to a radiological image detection apparatus and a method of manufacturing the same.
2. Related Art
In recent years, radiological image detection apparatuses employing an FPD (Flat Panel Detector) for detecting a radiological image and generating digital image data are utilized in practice, and spreading rapidly because the image can be checked immediately in comparison with the case of a conventional imaging plate. Such radiological image detection apparatuses of various types are proposed. An example of this is an indirect conversion type.
A radiological image detection apparatus of indirect conversion type has: a scintillator (a phosphor) formed from fluorescent material such as CsI (cesium iodide) for emitting fluorescence in response to radiation exposure; and a sensor panel constructed such that a plurality of photoelectric conversion elements and switching devices of thin-film type are arranged in two dimensions on a substrate. Radiation transmitted through an image-taking object is converted into light by a scintillator in the radiation image conversion panel. Then, the fluorescence from the scintillator is converted into electric signals by the photoelectric conversion elements in the sensor panel.
Further, a radiological image detection apparatus of so-called front face reading (ISS: Irradiation Side Sampling) type is also proposed that is obtained by modifying a radiological image detection apparatus of indirect conversion type such that radiation enters from the sensor panel side (for example, see Patent Document 1 (JP-A-7-27864)). According to this radiological image detection apparatus, the intensity of fluorescence of the scintillator emitted near the sensor panel increases and hence sensitivity is improved. This reduces the amount of exposure necessary for detection of a radiation image, and hence reduces the amount of exposure in an image-taking object.
Further, a technique is also proposed that a scintillator is constructed in the form of a group of columnar crystals obtained by crystal growth of fluorescent material such as CsI into columnar shapes by gas-phase deposition or the like (for example, see Patent Document 2 (JP-A-2011-017683)). Columnar crystals formed by gas-phase deposition do not include impurities such as binder, and further provides a lightguide effect of guiding the emitted fluorescence along the direction of crystal growth and hence suppresses diffusion of the fluorescence. This improves the sensitivity of the radiological image detection apparatus and improves the sharpness of the image.
Here, in the radiological image detection apparatus of ISS type, radiation is transmitted through the substrate of the sensor panel and then enters the scintillator. The substrate of the sensor panel is typically composed of glass. Nevertheless, glass absorbs radiation in not a little amount. This causes a concern of attenuation of the radiation entering the scintillator. Thus, in the radiological image detection apparatus described in Patent Document 1, the substrate of the sensor panel is composed of a resin sheet having a lower radiation absorbing power than the glass. Alternatively, even when glass is employed, a glass sheet as thin as a few 100 μm or the like is adopted.
When the substrate of the sensor panel is removed, attenuation of the radiation entering the scintillator is suppressed further. Nevertheless, when the substrate is peeled off, the moisture prevention effect obtained by the substrate is lost. Then, moisture enters the thin film constituting the photoelectric conversion elements and the switching devices and causes a concern that the photoelectric conversion elements and the switching devices are degraded.
Further, a possibility arises that moisture permeates through the thin film constituting the photoelectric conversion elements and the switching devices and then enters the scintillator. The CsI constituting the scintillator has deliquescence Thus, moisture absorption causes degradation in the characteristics of the scintillator. For example, in the scintillator constructed from a group of columnar crystals of CsI, the columnar crystal structure is damaged by moisture absorption. Thus, the above-mentioned lightguide effect is lost and the sharpness of the image is degraded.
Further, in the case of presence of the substrate, deliquescence of the scintillator caused by the entering of moisture begins at the periphery. In contrast, in a case that the substrate is peeled off, the entering of moisture into the scintillator occurs in the entire surface of the scintillator. Thus, a possibility arises that deliquescence progresses after beginning at the center part of the scintillator which overlaps with the effective imaging region of the sensor panel. The center part of the scintillator plays a major role in radiation image detection. Thus, a concern arises that in order that the diagnostic accuracy based on the radiation image should be maintained, frequent replacement of the scintillator becomes necessary.